Answer: R = 37.5 miles per gallon.
Explanation:
Sandras truck need one gallon to drive 25 miles, then the rate of Sandra's truck is 25 miles per gallon.
Her sister's car can travel 12.5 more miles with one gallon, so the car travels
25mi + 12.5mi = 37.5 miles with one gallon, the rate is
R = 37.5 miles per gallon.
Now, with that number you can multiply the amount of gallons that you have and you will obtain the total amount of miles that you can travel with that amount of gallons.